package indi.jp.project.core.util;

/**
 * 序列号工具类（使用雪花算法）
 *
 * 参考链接：https://github.com/beyondfengyu/SnowFlake
 *
 * @author jiangping
 * @date 2021/12/30
 */
public class SerialUtil {

    /**
     * 起始的时间戳
     */
    private final static long START_TIME_STAMP = 1640793600000L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 12L; //序列号占用的位数
    private final static long MACHINE_BIT = 5L;   //机器标识占用的位数
    private final static long DATACENTER_BIT = 5L;//数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    /**
     * 如果需要更多节点可以修改占位数来调整，最高可以设置10位机器位数（支持2的10次方，也就是1024台机器）
     */
    private long datacenterId;  //数据中心 0~31
    private long machineId;     //机器标识 0~31
    private long sequence = 0L; //序列号
    private long lastStamp = -1L;//上一次时间戳

    public SerialUtil(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     */
    public synchronized long nextId() {
        long currentStamp = getTimeStamp();
        if (currentStamp < lastStamp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currentStamp == lastStamp) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currentStamp = getNextMill();
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStamp = currentStamp;

        return (currentStamp - START_TIME_STAMP) << TIMESTAMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT             //机器标识部分
                | sequence;                             //序列号部分
    }

    /**
     * 重新获取时间戳，直到时间戳大于当前时间戳
     */
    private long getNextMill() {
        long mill = getTimeStamp();
        while (mill <= lastStamp) {
            mill = getTimeStamp();
        }
        return mill;
    }

    /**
     * 获取当前时间戳
     */
    private long getTimeStamp() {
        return System.currentTimeMillis();
    }

    /**
     * Main方法
     */
//    public static void main(String[] args) {
//        SnowFlake snowFlake = new SnowFlake(0, 0);
//        for (int i = 0; i < (1 << 12); i++) {
//            System.out.println(snowFlake.nextId());
//        }
//    }

}
